The present invention relates to a composition useful for reducing the strength of ice and to a method for treating frozen coal.
Many particulate materials such as coal are commonly stored or transported in open topped containers from which they must ultimately be removed. Any difficulty in readily and effectively removing the entire amount of the particulate material from the container represents a significant problem due to the time and trouble involved in overcoming impediments to such removal and the economic loss resulting in the event a significant portion of the material is not removed from the container.
In sub-freezing temperatures, the appreciable quantity of moisture commonly encountered in the storage and/or transporting of such particulate materials can hinder the efficient removal of the materials. Specifically, when the moisture on the particles freezes, the ice acts as powerful adhesive holding the particles together in a mass. It thus becomes difficult to unload or dump the particulate solid from the railway car, truck, or other transport container, thereby leaving a significant portion of the solid in the container. It also makes difficult the movement of coal from outdoor storage piles in a condition for fuel or other use. In addition, the moisture, upon freezing, causes the particulate material to freeze to the sides of the storage and/or transport container. This problem, often referred to as "slabbing", not only reduces the ability to effectively remove the particulate solid but can lead to derailments due to uneven weight distribution and high center of gravity.
Various techniques such as vibration, steam lances, fires under the railway cars, infrared heating in warming sheds and even dynamiting have been employed to heat or mechanically loosen the frozen particulate material. However, these techniques have only met with, at best, limited success due to their inherent safety problems, high costs and/or capital expense.
Other approaches which have been employed to reduce the problems associated with frozen coal include the use of chemicals which reduce the freezing point and/or the strength of ice. For example, salts such as sodium chloride and calcium chloride have been added to the moist coal as it is being loaded, i.e., prior to freezing, to reduce the freezing point of water. Unfortunately, relatively high concentrations of the salts have been taught as being necessary for effective performance. Although the salt, if added in sufficiently high concentrations and in the proper manner, will reduce the effects of frozen coal in dumping or unloading operations, its addition has not been found to substantially reduce the problems associated with the freezing of coal to the side walls of the transport or storage container. In addition, it has long been felt that the salts will cause significant corrosion problems.
Alternatively, oil has been added to the particulate material, preferably upon loading, with questionable success to "freeze proof" the particles. Oil soluble surfactants have also been used in combination with the oil with questionable results. Ethylene glycol, propylene glycol or a mixture thereof has also been employed to reduce the problems associated with the freezing of the particulate solids. Unfortunately, the amount of glycol required to reduce the freezing point of the resulting water/glycol solution by even a few degrees high is relatively large. Therefore, treatment using glycol can be costly and, in some cases, uneconomical. Moreover, the use of ethylene glycol and/or oils does not substantially reduce the slabbing or the freezing of the coal to the side walls of the transport or storage container.
A chemical composition, commonly referred to as a "freeze conditioning agent", which has been shown to be useful in reducing problems associated with frozen particulate solids is a composition of a water-soluble polyhydroxy compound or monoalkylether thereof and a water soluble organic nonvolatile compound such as sodium acetate. (See, for example U.S. Pat. Nos. 4,117,214 and 4,501,775). Such freeze conditioning compositions reduce the physical strength of ice, thereby facilitating the unloading and/or dumping of the treated particulate solid at freezing conditions. An equivalent freeze conditioning composition of the combination of a non- or slightly ionizing water-soluble organic compound such as a polyol and a compound containing an ammonium ion is described in U.S. Pat. No. 4,254,166. Although these freeze conditioning agents are very effective in reducing the problems associated with freezing of moisture, the higher amounts of moisture often encountered toward the outer portions of the transport and/or storage container dilutes their effect, thereby rendering the disclosed freeze conditioning agents less effective in this portion and requiring the use of additional means to fully remove the particulate materials from the container.
A thickened aqueous solution of a water-soluble polyhydroxy compound or monoalkylether thereof, a water-soluble organic nonvolatile compound and/or an inorganic salt is taught to be useful in thawing ice in U.S. Pat. No. 4,388,203. The thickener is added to the aqueous solution to increase the viscosity and tackiness of the composition sufficiently to maintain an essentially even coating of the composition when applied to a frozen surface. The preferred compositions contain both the water-soluble organic non-volatile compounds and the inorganic salt.
To reduce the problems associated with the particulate solids adhering to the side walls of the transport and/or storage containers, it has become a common practice to apply a chemical composition, often referred to as a "side release agent" to the containers prior to loading. The side release agents from a boundary between the ice and the side walls and allows the slabs of material to fall from the container during normal dumping. A representative side release agent is brine containing small amounts (i.e., up to 3 weight percent) of a polymeric ethylene oxide component of a molecular weight between 100,000 and 600,000 as described by U.S. Pat. No. 4,410,599. An alternative side release agent is disclosed in U.S. Pat. No. 4,338,359 as being a water solution of an inorganic freeze point depressant, e.g., calcium chloride, and a thickening agent, e.g., various methyl cellulose derivatives. Unfortunately, the use of side release agents is not often economical. In addition, except on short haul, captive rail car conditions, regardless of the effectiveness of the known side release agents on reducing the adhesion of the frozen slabs of material to the side walls, the use of a side release agent does not eliminate the need for the use of a freeze conditioning agent to prevent the bulk of particulate material from freezing into a single solid mass.